Scientific American citerer fra Mara Hvistendahls bog Unnatural Selection: Choosing Boys over Girls and the Consequences of a World Full of Men.

The technology that ultimately became the dominant method of sex selection around the world began as a tool for navigation. The story of ultrasound dates to 1794, when an Italian biologist curious about how bats find their way in the dark discovered sonar, or the fact that distance can be determined by bouncing sound waves off a faraway object and measuring how long it takes for the waves to ricochet back. Centuries later, when the growing prowess of German submarines during World War Iconvinced the Allies that to win the war they needed a way to navigate underwater, scientists put sonar to use. The American, British, and French governments jointly funded research into the phenomenon. The effort succeeded, and by 1918 the Allies were using acoustic echoes to correctly pinpoint the location of German U-boats.

After the war, doctors guessed sonar might have medical applications as well. They first used ultrasound in surgery, where it turned out sound waves could heat and destroy tissue, making them helpful for everything from treating ulcers to performing craniotomies. Then in 1949 a chemist stationed at the Naval Medical Research Institute in Bethesda, Maryland, employed the new technology to locate gallstones in dogs, and ultrasound became a diagnostic tool as well. Physicians began navigating the human body as World War I submarines had navigated dark waters, bouncing sound waves off the internal organs.

Ultrasound proved surprisingly versatile. It could clean teeth, treat cysts, and dissolve kidney stones. It may have been with one of these applications in sight that in 1959 Scottish obstetrician Ian Donaldused the new technology on a woman who happened to be pregnant and noticed that the fetus returned echoes as well.

Two images of cats — my favorite animal – were burned into my brain when I finished reading Mara Hvistendahl’s “Unnatural Selection: Choosing Boys Over Girls and the Consequences of a World Full of Men (PublicAffairs, 336 pages, notes, index, $26.99). One was of Puneet Bedi, a medical student in India, seeing a cat “bounding past him, a bloody blob dangling from its mouth.” Stray dogs and cats were common in Indian hospitals in 1978, but what Bedi saw in that cat’s mouth turned out to be an aborted fetus of a girl that was treated so casually — left on a tray where any stray animal could find it – ”because it was a girl,” a nurse told him.

The other cat image was that of Canadian geneticist, Dr. Murray L. Barr, one day in 1949 peering into a microscope at the cells of a female cat. What he saw was a tiny, previously unnoticed cellular body. “A quick survey of cells from other cats revealed only females had the body; males lacked it entirely.” Barr quickly realized the substance could be a shortcut around the sex chromosome problem. ”Like sex chromosomes, the cellular body indicated the sex of an organism. But unlike the chromosomes, it was relatively easy to detect….”

The discovery netted a nomination for a Nobel prize for Dr. Barr. It also was an easy way to determine the sex of an adult whose sex was uncertain, including masculine female Soviet athletes in the Olympics. But even more significant, it led to procedures that enabled doctors to determine the sex of a fetus, which in many cultures led to an abortion of the kind Dr. Bedi saw in that Delhi hospital.

On a trip several years ago to Lhasa, Tibet’s capital, I was captivated, like so many travellers, by the historical sites: the Potala Palace, residence of the Dalai Lamas; or the Barkhor, the warren of shops and holy sites in the town’s centre. But I also noticed a phenomenon I could not find in my guidebook: the city was dominated by men. Unemployed men lounged, drunk, in parks and bus stations. They patrolled the streets, and wandered through markets. For every ten I counted, I would see at most two or three women.

As science journalist Mara Hvistendahl shows in Unnatural Selection, a bracing work of investigative reporting, such scenes are increasingly common in developing nations. From China to India, to eastern Europe and the Middle East, sex ratios – the relative numbers of boy babies to girls – are becoming skewed. The norm should be around 105 boys for every 100 girls. But in China the ratio is around 121 to 100; in India and Vietnam 112 to 100; in Albania 110 to 100.

Within a decade China could have 30m men who cannot find wives, with the situation even more skewed in cities, like Lhasa, that attract migrant male labourers. These imbalances could prove as destabilising as climate change, potentially sparking crime, trafficking, and other wider conflicts.

Ms. Hvistendahl also dredges up plenty of unpleasant documents from Western actors like the Ford Foundation, the United Nations and Planned Parenthood, showing how they pushed sex-selective abortion as a means of controlling population growth. In 1976, for instance, the medical director of the International Planned Parenthood Federation, Malcom Potts, wrote that, when it came to developing nations, abortion was even better than birth control: “Early abortion is safe, effective, cheap and potentially the easiest method to administer.”

The following year another Planned Parenthood official celebrated China’s coercive methods of family planning, noting that “persuasion and motivation [are] very effective in a society in which social sanctions can be applied against those who fail to cooperate in the construction of the socialist state.” As early as 1969, the Population Council’s Sheldon Segal was publicly proclaiming the benefits of sex-selective abortion as a means of combating the “population bomb” in the East. Overall Ms. Hvistendahl paints a detailed picture of Western Malthusians pushing a set of terrible policy prescriptions in an effort to road-test solutions to a problem that never actually manifested itself.